Current data processing systems require circuit board packaging systems that are designed to be compact and easy to service and upgrade at the end-user cite. Such compact designs are necessary because they are easily utilized in office environments where the availability of space is limited or special environmental conditions are required by the data processing systems. In addition, data processing systems typically support a number of options, and the end user may wish to add or remove options at any time after an initial installation. It is desirable that the field service representative or an user be able to make these changes in the minimum time possible without the need for special tools.
A common method of achieving the goals of compact design and ease of field service and field upgrades is to employ a modular circuit board design. A common type of modular design provides for a main circuit board, also known as the mother board or backplane. The mother board usually provides, the basic computer circuitry that is essential for operation of the data processing system is located on the mother board. Also, connections to the mother board are provided so that additional circuit boards, known as daughter boards, can be used to provide optional or enhanced functions. An example of a family of computers employing such a modular circuit board design is marketed by the IBM Corporation under the trade name of the AS400 family of computers.
The AS400 family of computers houses daughter boards in packages known as book package assemblies. An example of such a prior art book package is depicted in FIGS. 1 and 2. An expanded view of the book package 100 of FIG. 1 is depicted in FIG. 2. Typically, a single circuit board 102, having connectors 114 and 116 for connection to the backplane, is housed within a structure formed from side coverage 104 and 106 and top and bottom rail assemblies 108 and 110, respectively. Latches 112 are provided to mechanically secure the book package into the chassis associated with the backplane.
The use of book package assemblies confers several benefits. For example, the circuit board housed therein is protected from electrostatic discharge (ESD) during handling by a service person. In addition, the housing structure is usually metallic which confers electromagnetic interference (EMI) shielding for the circuit board 102 housed therein. In addition, the book package 100 is more rugged than the circuit board 102 so that it can withstand the rigors of handling, i.e., those other than ESD, better than the naked circuit board 102 can withstand them.
In FIG. 4, a prior art book package 100 is depicted as plugging into a mother board 300 via a chassis 302. As a modular computer system, e.g., the AS400 family, develops, the manufacturer strives to maintain uniform dimensions for key components such as daughter boards and the chassis. One reason for this is that it minimizes some of the difficulties associated with retrofitting older models in the product line with enhancements and/or new options.
The enhancements and/or options might require circuitry that exceeds the space available on a single daughter card. In such a situation, the circuit has to be split into two separate daughter cards. Some prior art systems require the two parts of this oversize circuit to communicate via the backplane. This is a relatively long signal path that can introduce unacceptable signal propagation delays due to the length of the path. Some prior art systems, for example, U.S. Pat. No. 5,444,008 to Dimmick, Sobotta (one of the Inventors of the present invention) et al., filed Jun. 30, 1994, and issued Aug. 6, 1996, enclosed two daughter boards within a single book package and connected the daughter boards together by an edge connector in addition to the connection via the backplane.
The U.S. Pat. No. 5,544,008 patent provides a much easier access to the daughter boards than other prior art systems that provided plural boards within a single book package. Consequently, if one of the plural boards failed, the U.S. Pat. No. 5,544,008 patent made it much easier for a service person to open the book package, remove the defective board, replace it, and then re-assembly the book package.
Unfortunately, the U.S. Pat. No. 5,544,008 patent still requires a service person to open the book package, which exposes the non-defective board to the risks of handling by the service person, i.e., ESD damage to the electrical components and mechanical damage from the rigors of handling. Moreover, the U.S. Pat. No. 5,544,008 patent suffers from a relatively long path length connecting the first daughter board to the second daughter board because of the requirement of connecting via the edge connector provided in addition to the backplane connections. In addition, the process according to the U.S. Pat. No. 5,544,008 patent by which a defective board in a book package is replaced remains relatively lengthy because of the need to open the book package, unplug the defective board, plug in the replacement board, and re-close the book package, in addition to the steps of removing the book package from the backplane and then re-attaching it to the chassis backplane.
An example of how a prior art latch 112 is attached to the book package 100 is depicted in FIG. 3. In FIG. 3, a latch retainer 204, for example, made of stainless steel, is attached to the side covers 104 and 106. The latch 112 is retained by inserting latch pins 200 integrally formed on the latch 112, into the holes 202 in the retainer 204. A stud 206 is inserted in a coil spring 208 such that an end 210 of the stud 206 engages a flat surface 212 on the stud 206. The spring-biased stud 106 is inserted in the retainer 204 so that the flat surface 212 addresses the D-shaped hole 214 that will be next to the cover plate 216. A small diameter pin-like extension 218 of the stud 206 is inserted into a hole 220 on the cover plate 104 and a tab 222 on the retainer 204 is inserted into a slot 223 in the cover plate 104. The stud 206 is then rivetted to the base cover 106, securing the assembly. These same parts, using a mirror image coil spring 210, are similarly assembled in the other latch position.
The latch assembly of book package 100 differs from that shown in FIG. 3, for example, because the latch retainer 204 is integrally formed from the rails 108 and 110, respectively, and because the stud 206 has two pin-like extensions 218, i.e., no rivet is used to hold the studs 206 in place.